Electrically operable horn



3 1949- x R. H.-PURDEN 2,480,261

ELECTR'ICALLY OPERABLE HORN Filed Feb. 26, ,1947

In?) enter 7 Patented Aug. 30, 1949 ELECTRICALLY OPERABLE HORN RobertHesketh Purden, Birmingham, England, assignor to Joseph Lucas Limited,Birmingham,

England Application February 26, 1947, Serial No. 730,999 In GreatBritain March 15, 1946 2 Claims.

This invention relates to motor vehicle and other horns of th kind inwhich the air column is contained in a spiral sound cavity terminatingat one end in an open mouth, and in which the required vibrations in theair column are produced by a vibratory diaphragm, the latter beingactuated by an electromagnet. The object of the invention is to providean improved construction enabling a more compact design to be obtainedthan heretofore.

The invention comprises the combination of a body part formed. with aspiral sound cavity, and an electromagnet accommodated Within a boreformed at the centre of the said cavity.

In the accompanying drawings:

Figure 1 is a sectional side elevation and Figure 2 an inverted plan(with nd cover removed) showing a horn constructed in accordance withthe invention.

In carrying the invention into effect in the manner shown by thedrawings, I employ a circular and shallow body part a, the diameter andthickness (or axial length) of which is sufficient to permit theformation therein of the required spiral sound cavity b. The outer endof this cavity terminates in a flared mouth piece 0. For convenience ofmanufactur the spiral cavity is open to a flat side of the body part,and is closed by a cover flat plate (1 attached to that side. The cavityb shown in the drawings forms no part of the sound cavity b and servesonly to reduce the mass of metal required in the body part. But if it isdesired to giv the horn a lower pitched tone, the cavity b may form anextension of the sound cavity 1). In this case the bridge piece I)separating the cavities b, b is machined out. The

.vibratory diaphragm e is secured at the other side of the body part,and the make-and-break device I which controls the electromagnet islocated outside the diaphragm, this device being enclosed by a coverpiece g detachably secured to the body part. The region bounded by oneside of the diaphragm communicates with the inner end of the spiralcavity 1) through an opening it (Figure 2). It will b understood thatwhen the cavity 11 forms an extension of the cavity b as above describedthe opening it will be arranged at the end of the cavity 12 remote fromthe cavity 12.

, The essential feature of my invention resides in the mode ofaccommodating the electromagnet. According to my invention I form in thebody part a a bore situated at th centre of the spiral cavity, that isto say this bore is surrounded by the said cavity, and the electromagnet(consisting of an iron core 2' and surrounding winding 1) is mounted inthis bore, the core 1' being 'adjustably secured to the cover plate d bya screw-thread connection and lock nut k. The required magnetic actionto be exerted on the diaphragm e is effected through the medium of aniron armature m attached to the centre of the diaphragm and situatedadjacent to one end of the core i.

By 50 arranging the electromagnet, I am able to efiect a desirablereduction in the overall dimensions of a horn for a given duty, and thusobtain a more compact design than is practicable with the constructionshitherto employed.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. An electrically operable horn comprising in combination a body partformed with a spiral tubular sound cavity around a central bore, anelectromagnet having an iron core and accommodated within the bore inthe body part, and a diaphragm situated at one side of the body part,the inner end of the cavity being in communication with the regionbounded by the inner side of the diaphragm, and the outer end of thecavity being open.

2. An electrically operable horn comprising in combination a body partformed with a spiral sound cavity around a central bore, anelectromagnet having an iron core and accommodated within the bore inthe body part, a diaphragm situated at one side of the body part, and acover plate attached to the body part and closing one side of thecavity, the inner end of the cavity being in communication with theregion bounded by the inner side of the diaphragm, and the outer end ofthe cavity being open.

ROBERT HESKE'I'H PURDEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

